1. Field of the Invention
The invention relates primarily to new compositions comprising aromatic polyimides containing terminally unsaturated amide groups as part of hemi-amic acid or derivative groups. More specifically, it relates to such compositions in which the terminal amide groups are moieties that contain terminal CH.sub.2 .dbd.CH-- functions capable of polymerizing and forming cross-linked polymers. Still more specifically, it relates to such polyimide hemi-amic acid groups and to the crosslinked polymers obtained therefrom without the formation of by-products.
2. State of the Prior Art
Polyimides, as prepared from aromatic dianhydrides and aromatic diamines, are known to have the desired property of high heat resistance and high solvent resistance. Such polyimides, upon condensation to an infusible condition, generate by-products such as water and other vapors or gases which introduce voids into the fabricated products that detract from the expected good physical properties. In addition, because of these same desirable properties, they are untractable and therefore very difficult and expensive to work into desired shapes and forms.
Recent patents, such as U.S. Pat. Nos. 3,879,395 and 3,998,786, are directed to improving the tractability of the aromatic polyimides by attaching various terminal groups to polyimide oligomers whereby the chains are extended by coupling of the terminal groups. In both of these patents the coupling groups are attached as terminal imide moieties containing vinyl, propargyl, nitrile, etc. groups. Thus the terminal anhydride group is converted to an imide group containing a vinyl, nitrile, propargyl, etc. group. However in neither of these patents nor in any other related prior art reference has there been found any disclosure that the terminal anhydride group on each end could be converted to one amide moiety and a second amide or acid or ester moiety of which at least one or both could contain polymerizable structures. The amide groups present in the polyimide derivatives of this invention are tertiary amides devoid of hydrogen or the amide nitrogen. Therefore on heating, these amide groups do not convert to imide structures with accompanying by-product formation and simultaneous loss of crosslinking functionality. Consequently these structures contribute higher tractability to the composition and control of the number of crosslinking groups to values up to four with functionalities up to eight.